Photosensitized Decomposition of Acetyl PeroxideC. Luner and M. Szwarc Citation: The Journal of Chemical Physics 23, 1978 (1955); doi: 10.1063/1.1740646 View online: http://dx.doi.org/10.1063/1.1740646 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/23/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Photolysis of Acetone in the Presence of HI and the Decomposition of the Acetyl Radical J. Chem. Phys. 36, 2196 (1962); 10.1063/1.1732851 Kinetics of the Decomposition of Diethyl Peroxide J. Chem. Phys. 20, 574 (1952); 10.1063/1.1700495 Decomposition of Benzoyl Peroxide in a Magnetic Field J. Chem. Phys. 17, 741 (1949); 10.1063/1.1747381 The Mercury Photosensitized Decomposition of Ethane J. Chem. Phys. 6, 179 (1938); 10.1063/1.1750223 The Mercury Photosensitized Decomposition of the Deuteroammonias J. Chem. Phys. 2, 373 (1934); 10.1063/1.1749491

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1978 LETTERS TO THE EDITOR

, , ,

\\"""

wove fundlDn, "V

charge dlst"buflon, .__-----, \jI2(~2_~2)

\ "I"" ~ ............................ .. \,t/ - ......... __

FIG. 1. Wave function and charge distribution along dipole axis.

A few further remarks may be of interest. As there is no R dependence at constant moment, the coefficients of the terms of the series that are the wave functions likewise are independent of R. The first terms of the series give, approximately, aside from a normalization factor

f"'e-p(HI') .

This, from the definition of A and p., is

f"'e-Prl' R,

a hydrogen-like orbital on the positive charge. The effective charge parameter varies as l/R, as indeed it should. On this basis it appears reasonable that the electronic energy should approach - 00, since the electron may stay in the left half of space, and thus be in the region of a high positive potential, as R approaches zero.

It is worth noting that a mathematical dipole potential is extra­ordinary in this respect. Representing a general multipole poten­tial as

V= - (qn/rn)Pn_I(cosfJ),

where n= 2 for a dipole, 3 for a quadrupole, etc., and a trial eigenfunction as

f=rme-arf(()

on dimensional grounds, the kinetic energy is of the form 00', and the potential energy -ban. We have

E=aa2-ban.

Minimizing with respect to a,

an-'= 2a/nb,

which misbehaves for n= 2. This argument implies nothing about the higher multipoles, as the variation theorem provides only an upper bound to the energy.

E' was calculated for various values of ~ using appropriate ex­pressions from the Baber and Hasse paper.! Calculations were performed for the ground state only and are good to about 10%.

Dipole moment, ~ Atomic units Debyes

o 0 0.3 0.76 0.5 1.27 0.7 1.78

4p' Atomic units

(R in Bohr radii)

1 0 1.4 XIO-' 2.1 XIO-' 1.2 XIO-'

. egs units (R in A)

o 1.1 XIO-' 1.6 X 10-' 9.1 XIO-'

1 Baber and Hasse, Proc. Cambridge Phil. Soc. 31, 564 (1935).

Photosensitized Decomposition of Acetyl Peroxide c. LUNER AND M. SZWARC

Chemistry Department, State University of New York, College of Forestry, Syracuse 10, New York

(Received July 25, 1955)

I T appears that aromatic hydrocarbons may act as photo­sensitizers for a variety of reactions proceeding in solution.

For example, West and Miller! have shown that certain aromatic

hydrocarbons may sensitize the decomposition of alkyl halides in hexane solution. Recently, a number of papers2-4 dealing with the sensitized fluorescence of aromatic hydrocarbons with ultra­violet and 'Y rays have appeared. In this note, the decomposition of dilute solutions of acetyl peroxide photosensitized by aromatic hydrocarbons is reported.

When a degassed solution of acetyl peroxide in benzene (10-3 M) was irradiated with light of the wavelength 2537 A, obtained from a mercury resonance lamp combined with a Corning 7910 filter, acetyl peroxide was decomposed. Similar results were obtained by irradiating with the 3650 A line dilute solutions of acetyl peroxide in iso-octane containing small amount of anthracene or naph­thacene. Since at 2537 A, benzene essentially absorbs all the exciting radiation, while at 3650 A only the aromatic hydrocarbon absorbs the radiation (acetyl peroxide does not absorb in this region), it must be concluded that the aromatic hydrocarbon sensitizes the decomposition of acetyl peroxide.

Preliminary quantitative experiments were performed with anthracene as the sensitizer and the 3650 A Hg line as the exciting radiation. The data are given in Table I. The rate of decomposition of acetyl peroxide, measured by the rate of formation of carbon dioxide, seems to be proportional to the concentrations of acetyl peroxide and anthracene. This relation is shown in Fig. 1. How­ever, at concentration of anthracene exceeding 1.10-4 M, the rate of decomposition levels off. It was calculated from the extinction coefficient of anthracene at 3650 A, that 99% of the radiation is absorbed at the concentration of 1.5.10-4 M. It should, therefore, be expected that at higher concentrations of anthracene, the rate of decomposition would be independent of its concentration.

Table I shows that the CH4/CO Z ratio decreases with increasing concentration of anthracene. This effect is similar to that observed by Levy and Szwarc5 who studied the thermal decomposition of acetyl peroxide in the presence of aromatic hydrocarbons, and showed that the decrease in the ratio was due to the addition of methyl radicals to the aromatic compounds. A similar interpreta­tion would apply here.

In many photochemical or photosensitized reactions, radicals are formed in the primary process. The rate of such reactions is usually deduced from the rate of formation of specific products resulting from the subsequent reactions of the radical. The present investigation shows how misleading such a conclusion might be if the rates were based on the rate of formation of methane. In this investigation, complications of such a nature are avoided by using the rate of formation of CO 2 as a measure of the rate of decomposi­tion of the peroxide.

While the ratio CH,/CO. decreases considerably with increasing anthracene concentration, the ratio C2H,/C02 remains essentially­constant, independent of acetyl peroxide and anthracene concen­tration, and of light intensity. These results indicate that ethane is formed by a cage reaction. Similar results were obtained in the thermal decomposition of acetyl peroxide in the presence of a variety of scavengers.' In the latter work, the ratio of CzH,/COz was found to be 0.084 at 65°C and 0.045 at 85°C, while an average value of 0.13 at 25°C was found in the present study. This result is in accord with the concept of a cage reaction, the higher ratio

TABLE 1. Photosensitized decomposition of acetyl peroxide in iso-octane at 25°C.

Acetyl peroxide Anthracene RC02 CH, C,H. MXI03 MXIO' M/hrXIO' CO, CO,

1.6 0.28 0.20 0.62 0.11 1.6 0.72 0.58 0.58 0.12 1.6 1.45 0.90 0.59 0.13 1.6 4.35 1.17 0.46 0.12 3.2 4.35 1.80 0.54? 7.2 4.35 3.54 0.45 0.13 7.2 9.43 3.21 0.43 0.13 7.2 18.8 3.10 0.39 0.13 1.6- 0. 72 0.25 0.61 0.14

- Incident intensity reduced by 38%.

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LETTERS TO THE EDITOR 1979

o

'0

'" x , ~ 20

'" ~ 0 :>

"'0 0

10

ANTHRACENE CONCENTRATION 4.35 X IO-"M

N

8 "0 z 0

~ .. :>

'" :;: "0

'" ~ :

0

10

o.

FIG. 1.

ACETYL PEROXIDE CONCENTRATION

1.6 X I<r'M

o

obtained at 25°C reflects the greater probability of cage recom­bination of radicals at lower temperatures. It would thus appear that the photosensitized decomposition of acetyl peroxide in­volves a mechanism similar to that operating in the thermal decomposition.

Further experiments are in progress and will be reported at a later date.

1 W. West and W. E. Miller, J. Chern. Phys. 8, 849 (1940). 2A. Weinreb and S. G. Cohen, Phys. Rev. 93, 1117 (1954). 'H. Kallmann and M. Furst, Phys. Rev. 79, 857 (1950). 'E. J. Bowen and R. Livingston, J. Am. Chern. Soc. 76,6300 (1954). 'M. Levy and M. Szwarc, J. Am. Chern. Soc. 77, 1949 (1955). 6 A. Rembaum and M. Swarc, J. Am. Chern. Soc. 77, 3486 (1955).

Supplementary Comments on the "Electronic Structure of the Amylose-Iodine Complex"

HIDED MURAKAMI

Department of Chemistry, Faculty of Science, Osaka University, Osaka, Japan (Received July IS, 1955)

I N a previous paper,' the author discussed the charge transfer from hydroxyl- or bridge-oxygen atoms into the iodine chain

with respect to the electronic structure of the colored molecular complexes between iodine and oxygen-containing organic mole­cules such as amylose,.(·) a-dextrin (cyclohexaamylose),3 pyrone derivative,3 and polyvinyl alcohol.' As can easily be inferred, the electronic interaction between oxygen and iodine amounts to appreciable value only when the relative configuration between two components allows the sufficient approach of these atoms. In case of polyvinyl alcohol- or pyrone derivative-iodine complex, it seems to be no apparent difficulty to realize the required relative configuration between two components.

On the other hand, in case of amylose- or a-dextrin-iodine complex, it was found such an ambiguity as follows on this point. In a previous paper, the author adopted one of the possible chair forms of pyranose ring in the glucose residue* [chair form (I), see Fig. 1 (b) in reference 1]. According to the result of x-ray analysis, however, the pyranose ring in the crystalline sucrose exists as another chair form (II). 5 If the latter form (II) is adopted into the helical amylose, the distance between the internal iodine and

hydroxyl oxygen in the primary alcoholic group (or bridge oxygen in the pyranose ring) becomes considerably larger compared with the author's previous model. Consequently, one can scarcely expect the electronic interaction between iodine and these oxygens.

One should notice, however, the existence of the other oxygen atoms of which one can expect some amount of electronic inter­action with the internal iodine. These oxygen atoms exist as the connecting bridge between neighboring pyranose rings (glucosidic oxygen). At present, the experimental data are not sufficient to predict the very accurate atomic coordinates in the helical amylose even when the stereochemical form of the pyranose ring is postulated as chair form (II). Consequently, the geometry of helical amylose is examined by using the following two idealized models·t

Model (1): the bond angles of all the carbon (and oxygen) in the pyranose ring are assumed to be tetrahedral angle. In this case, all the strain is comcentrated into the bond angle of glucosidic oxygen and makes it abnormally large. (The projected value of this angle on the plane which is normal to the helical axis is about 127°, and the actual bond angle slightly exceeds 130°.) The projected figure shows that the internal surface of helix is dom­inated by hydrogen atoms and oxygen atoms cannot contact with the internal iodine. (The exterior van der Waals' diameter of this helix is estimated as 13.7 A2(b).)

Model (2): the actual (not projected) bond angle of glucosidic oxygen is kept to tetrahedral angle and the major part of the strain is transferred into the other parts of amylose. By adjusting the valence angles of carbon atoms within the reasonable range so as to give the observed exterior van der Waals' diameter 13 A,2(e) the dominance of hydrogen atoms in the internal surface of helix is removed and the oxygen atoms are brought on the contact with iodine.

Consequently, if the actual geometry of helical amylose is close to model (2), one can expect the electronic interaction even when the chair form (II) is adopted. Here, one should consider that such a configuration as model (2) is stabilized by the electronic inter­action energy between oxygen and iodine even if it includes some amount of strain. In this configuration, the hydroxyl oxygen in the secondary alcoholic group (CH20H) may also be able to contact with the internal iodine more or less. Thus, the essential part of the previous paper seems to retain its validity. The detailed study on the geometry of helical amylose will be reported elsewhere.

1 H. Murakami, J. Chern. Phys. 22, 367 (1954). 2 (a) R. S. Stein and R. E. Rundle, J. Chern. Phys. 16, 195 (1948). See

also R. J. Hach and R. E. Rundle, J. Am. Chern. Soc. 73, 4321 (1951). (b) R. E. Rundle and F. C. Edwards, J. Am. Chern. Soc. 65, 2200 (1943). (c) R. E. Rundle and D. French, J. Am. Chern. Soc. 65, 1707 (1943).

3 F. Cramer, Chern. Ber. 84, 855 (1951); H. v. Dietrich and F. Cramer, Chern. Ber. 87, 806 (1954). See also F. Cramer, Chern. Ber. 86, 1576, 1582 (1953).

'c. D. West, J. Chern. Phys. 15,689 (1947). * The author's previous statement is due to the oversight of some of the trans-configurations and is not correct.

'C. A. Beevers and W. Cochran, Proc. Roy. Soc. (London) A190, 257 (1947).

t In the present examination, it was assumed that the helical amylose contains exactly the six glucose residues per turn although slight deviation from this statement seems to be permissible.

Sensitivity of Explosives to Pure Shocks WILLIAM A. GEY AND ARTHUR L. BENNETT

U. S. Naval Ordnance Test Station, China Lake, California (Received May 12, 1955)

T HE "influence" test of sensitivity of explosives to explosive shocks is a valuable criterion for determining the suitability

of explosive components in explosive applications.' We have undertaken an investigation of the initiation of

reaction of explosive materials by uniform shocks in a shock tube. The use of the forward facing shock in an inert atmosphere appears to provide a reproducible experimental determination of

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